What's the point of portal exactly?

It seems even when my portal is still open and I go through it it starts me back at the beginning of the map? I thought the point of the portal was to take you to town and exactly back to where you opened it? When did this start? Now I have to do this long for no reason map all over again. This campaign is just Way TOO LONG! and y'all are going to make it even longer!?!? Seriously? Idk if I can do another character through this again.